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Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11
Graphical Abstract
Figure 1: Examples of amino-functionalized 1,2-oxazole derivatives I–VIII.
Scheme 1: Conversion of cyclic amino acids to 1,2-oxazole derivatives.
Scheme 2: Plausible mechanisms for the formation of 1,2-oxazoles 4a–h and VII from β-enamino ketoesters 3a–h ...
Figure 2: (a) 1H NMR (italics), 13C NMR (normal), and 15N NMR (bold) chemical shifts (ppm) of compound 3a in ...
Scheme 3: Synthesis of compound 15N-1,2-oxazole 5. The coupling constants of JHN and JCN from 15N2 are indica...
Figure 3: Stacked chromatogram view of pairs of enantiomers with area, %: (R)-4b, ee 100% (tR = 10.1 min) and...
Figure 4: (a) Structure of 4b with syn- and anti-conformers; (b) superimposed 1H NMR and 1D gradient NOE spec...
Scheme 4: Synthesis of 2-[4-(methoxycarbonyl)-1,2-oxazol-5-yl]cycloaminyl-1-ium trifluoroacetates 6a,b.
Figure 5: ORTEP diagram of the asymmetric unit consisting of two cations 6b(A) and 6b(B) and triflate anions.
Beilstein J. Org. Chem. 2019, 15, 679–684, doi:10.3762/bjoc.15.62
Scheme 1: Preparation of hydroxyalkynyl substrates from 1-phenyl-1H-pyrazol-3-ol (1).
Scheme 2: Cyclization of hydroxyalkynyl substrates to 2,5-disubstituted 2H-furo[2,3-c]pyrazoles.
Figure 1: a) ORTEP diagram of the asymmetric unit consisting of two independent molecules 4d(A) and 4d(B); b)...
Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110
Scheme 1: Envisaged approach for the synthesis of 5-chloropyrazole-4-carboxylates 2.
Scheme 2: Synthesis of bipyrazolone 3a.
Figure 1: Signal of the OCH2 ester protons of reaction product 3a (500 MHz, CDCl3).
Figure 2: ORTEP-plot of the crystal structure of compound 3a drawn with 50% displacement ellipsoids [(4S,4'S)-...
Figure 3: Arrangement (4R,4'R)- and (4S,4'S)-3a enantiomers in the crystal unit drawn with 50% displacement e...
Scheme 3: Synthesis of compounds 3a–i.
Scheme 4: Reaction of different 5-hydroxypyrazoles with thionyl chloride.
Scheme 5: Reaction of 1a with sulfuryl chloride.
Scheme 6: Possible reaction mechanism for the transformation 1 → 3.
Scheme 7: Preparation of bipyrazoles 10.
Figure 4: 1H NMR (italics), 13C NMR (normal letters) and 15N NMR (in bold) chemical shifts of 3a (in CDCl3).